A Union

(countable) The act of uniting or joining two or more things into one. Synonyms: A Junction, A Coalition, A Combination Antonyms: A Nonunion, A Disunion
(uncountable) The state of being united or joined; a state of unity or harmony. Antonyms: A Nonunion, A Disunion
(countable) Something united, or made one; something formed by a combination or coalition of parts or members; a confederation; a consolidated body; a league.
(countable) A trade union; a workers' union.
(countable) An association of students at a university for social and/or political purposes; also in some cases a debating body.
(countable) A joint or other connection uniting parts of machinery, such as pipes.
(countable, set theory) The set containing all of the elements of two or more sets.
(countable) The act or state of marriage.
(uncountable, archaic, euphemistic) Sexual intercourse.
(countable, programming) A data structure that can store any of various types of item, but only one at a time.
(countable, now rare, archaic) A large, high-quality pearl.
(historical) An affiliation of several parishes for joint support and management of their poor; also the jointly-owned workhouse.